I am accustomed to using SQL Sever to directly design the database every time, but do not pay enough attention to SQL statements. I took the opportunity of this reconstruction of the computer room cooperation version to use SQL statements to design the database and at the same time Let’s sort out the basic usage of SQL statements.
【Classification】
There are 9 types of SQL statements, which can be roughly divided into 4 types according to their functions:
1. Query statement: select ----The most commonly used statement in the database
2. Data definition: create, drop, alter----for Operations on databases, data tables, and fields in tables
3. Data manipulation: insert, update, delete----the legendary "add, delete, modify, query", for specific Data operations
4. Data control: grant, revoke----definition and deletion of permissions
If you have learned the operating system, you will not be very familiar with these definition statements. Strangely enough, a database group file is also a kind of file and needs to have a logical name (i.e. file name), physical name (actual storage address on the disk), file size, etc.; the log file records all logical operations in the database, with details such as advantages and disadvantages. For the content, see Baidu Encyclopedia: Log file
[cascade|restrict] --Delete table, with constraints Restrict
must be added to the condition
3. Query statement:
Regular The query statement is: select * from datatable
It should be noted that nested and connected queries are queried from multiple tables. This combination relationship is commonly used in M:N relationships. Find the corresponding relationship.
select TB1.column1,TB1.column2
from TB1
where TB1.column1 in（select column1
from TB2
where TB2.column2="特定值"）；
Copy after login
This relationship is not recommended for users with confusing logic, as it is particularly likely to cause search failure.
set ##5. Embedded SQL usage technology, commonly used execution views, stored procedures, etc., add exec to execute
[Summary]
Knowledge is always like this , you will gain different results every time you study, especially after using it, you will try to compare the differences between different methods. I look forward to the next comparative study of database views, stored procedures and security settings.
The above is the content of a large collection of MySQL sql basic statements. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.
You can open phpMyAdmin through the following steps: 1. Log in to the website control panel; 2. Find and click the phpMyAdmin icon; 3. Enter MySQL credentials; 4. Click "Login".
MySQL and SQL are essential skills for developers. 1.MySQL is an open source relational database management system, and SQL is the standard language used to manage and operate databases. 2.MySQL supports multiple storage engines through efficient data storage and retrieval functions, and SQL completes complex data operations through simple statements. 3. Examples of usage include basic queries and advanced queries, such as filtering and sorting by condition. 4. Common errors include syntax errors and performance issues, which can be optimized by checking SQL statements and using EXPLAIN commands. 5. Performance optimization techniques include using indexes, avoiding full table scanning, optimizing JOIN operations and improving code readability.
Redis uses a single threaded architecture to provide high performance, simplicity, and consistency. It utilizes I/O multiplexing, event loops, non-blocking I/O, and shared memory to improve concurrency, but with limitations of concurrency limitations, single point of failure, and unsuitable for write-intensive workloads.
MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.
Creating an Oracle database is not easy, you need to understand the underlying mechanism. 1. You need to understand the concepts of database and Oracle DBMS; 2. Master the core concepts such as SID, CDB (container database), PDB (pluggable database); 3. Use SQL*Plus to create CDB, and then create PDB, you need to specify parameters such as size, number of data files, and paths; 4. Advanced applications need to adjust the character set, memory and other parameters, and perform performance tuning; 5. Pay attention to disk space, permissions and parameter settings, and continuously monitor and optimize database performance. Only by mastering it skillfully requires continuous practice can you truly understand the creation and management of Oracle databases.
The SQL INSERT statement is used to insert data into a table. The steps include: specify the target table to list the columns to be inserted. Specify the value to be inserted (the order of values must correspond to the column name)
